This invention relates in general to a method for the hydrogenation of silicon tetrachloride and more specifically to a high pressure plasma (HPP) method for the hydrogenation of silicon tetrachloride to produce trichlorosilane.
Trichlorosilane is the most widely used silicon source gas for the production of polycrystalline silicon. SiHCl.sub.3 is reduced with hydrogen at an elevated temperature to deposit pure polycrystalline silicon. By-products of this reaction are unreacted SiHCl.sub.3, SiCl.sub.4, HCl, other chlorosilanes and polymeric chlorosilanes. Less than about one third of the input SiHCl.sub.3 is converted to silicon and about two thirds is converted to SiCl.sub.4. The SiCl.sub.4 cannot be used efficiently for polysilicon growth and thus is essentially a low-value waste product. Attempts have been made to convert silicon tetrachloride to trichlorosilane; that is, to convert the waste material SiCl.sub.4 to a useful starting material SiHCl.sub.3. In one such attempt, SiCl.sub.4 is converted to SiHCl.sub.3 in a hydrogen reaction at high temperatures (1000.degree.-1200.degree. C.) and at high reactor pressures (typically 30-50 atmospheres). In this conversion, however, conversion efficiency and throughput are too low to be practical. Another problem encountered is that of silicon deposition in the hydrogenation reactor during the conversion.
Accordingly, a need existed for a method of converting silicon tetrachloride to trichlorosilane in order to reduce the cost of starting materials and thereby to reduce the cost of polycrystalline silicon. It is therefore an object of this invention to provide an efficient method for converting silicon tetrachloride to trichlorosilane.
It is a further object of this invention to provide a high pressure plasma method for the hydrogenation of silicon tetrachloride.
It is still another object of the invention to provide a method for the hydrogenation of silicon tetrachloride capable of high throughput and without silicon deposition during the conversion process.